Thursday, December 7, 2006

Transition Thursday; The "S" Word?

Now

Sunny, breezy, turning colder. After temperatures reached an unexpectedly high 56° around noon, the first phase of a double-barreled cold front passed through the metro area, lowering readings mainly into the 40s by early afternoon. At 4pm, Leesburg and Winchester were even into the upper 30s.

By mid afternoon, scattered snow flurries on radar were moving eastward, but only as far as I-81. To mix a metaphor, the other shoe drops tonight, when the Arctic air west of the mountains will come into the region on strong northerly winds. The "S" word of the day is "slight", as in chances of a light flurry east of the Blue Ridge.

Surface weather map at 1pm today from HPC/NCEP/NWS

Tonight and Tomorrow

Much colder. Tonight will be windy and cold under clearing skies; lows will be in the low to mid 20s. There is a slight chance of a passing snow flurry through this evening. Tomorrow will be sunny and brisk, windy with highs only near 36°.

For the weekend outlook and beyond with Larson's Long-Range, scroll down to Josh's post below.

El Niño Update

The NOAA/NCEP/Climate Prediction Center (CPC) today published the monthly El Niño Diagnostic Discussion. As shown in the chart, sea surface temperature anomalies have continued to increase in the tropical Pacific. In the month ending last week, the maximum departures from the long-term average were over 2°C (red area) near the International Date Line.

The outlook calls for the El Niño conditions to continue to increase through the winter months, followed by weakening from March to May next year. CPC's Dr. Vernon Kousky said that "typical El Niño effects over the U.S. during January through March 2007" can be expected. These effects are reflected in the NOAA winter outlook, which calls for near to above normal temperatures and near normal precipitation in the Mid Atlantic region, with the polar jet stream remaining primarily in Canada.

The CPC analysis is consistent with the latest report from the UN's World Meteorological Organization (WMO). The WMO notes that El Niño impacts are already significant in the western Pacific, with severe drought occurring in Indonesia and Australia, where the worst conditions in a century are impacting economic growth. Eastern equatorial Africa is also being affected, but by flooding from heavy rains.